The invention is concerned with a presser device for a sewing machine; more specifically with a means for varying the pressure exerted by a presser foot attached to a presser bar, and for lifting the presser foot from contact with a work material.
Generally, in the prior art, a compression spring is used to urge an endwise movable presser bar having a presser foot at one end thereof in contact with a work material, pressing the work material against feeding dogs in the bed of a sewing machine. Variation in the force which the presser foot exerts in pressing the work material against the feeding dogs is accomplished by varying the compression of the compression spring bearing on the presser bar. Increased force is required where the feeding dogs must feed heavy work material, or work material of many plies, or where the sewing machine operates at very high speeds causing the compression spring to "float" due to its own inertia, the result of rapid compressions thereof by the rising feeding dogs. Thus, the force exerted by the presser bar may be quite substantial.
In the usual sewing machine, the presser bar and presser foot attached thereto is brought to an elevated condition in order to remove or introduce work material between the presser foot and the feeding dogs, by means of a lever pivoted on the sewing machine frame and having a cam surface brought into contact with an abutment member fixed to the presser bar. When this lever, which normally projects from a rear surface of the sewing machine, is rotated, the cam surface thereof bears against the abutment member and urges it, and the presser bar to which it is attached, in an upward direction, further compressing the compression spring. In an appropriate circumstance, for example, where many plies of heavy fabric are being stitched at very high speeds, the amount of force required of a machine operator to elevate the presser foot from the work material may well be prohibitive. In other circumstance, where frequent manipulation of the lever is required, it may be found to be excessively tiring.
What is required is a presser device wherein the pressure exerted by a presser foot may be readily varied as required with little or no effect on the ease with which the presser foot may be lifted to an elevated position facilitating removal or insertion of a work material therebeneath.